Process of treating copper-bearing sands



C. H. BENEDICT AND H.l C. KENNY. PROCESS 0F TREATING COPPER BEARING SANDS.

APPLICATION FILED OCT. 7', I9I9.

Patented Mar. 30, 1920.

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L HIL UNITED sTATEs PANT oEEroE.

CENTENNIAL HARRY BENEDICT AND HERMAN C. KENNY, OF LAKE LINDEN, MICHIGAN.

PROCESS 0F TBETING COPPER-BEARING- SANDS.

To all lwhom t may concern Be it known thatv we, (1) CENTENNIAL HARRY BENEDIGT and (2) HERMAN C. KENNY, citizens of the 'United States, residing at (1) Lake Linden, (2)'Lake Linden, in the county of (l) Houghton, (2) Houghton, andv State' of (1) Michigan, (2) Michigan, have invented certainnew and useful Improvements inProcesses of Treating Copper-Bearing Sands, of which the following is a specification. 4

It is well known that in the leaching of copper-bearing sands or the like with solutions containing ammonia, usually employed in conjunction with cupric salts, mam terial losses 'of ammonia are encountered owing to the tendency of the sands to` occlude or adsorb ammonia, thequantity of ammonia so adsorbed being in general approximately proportionate to the concentration of the ammoniacal solutions. The adsorbed ammonia cannot be completely recovered by simple washing with water either at normal or higher temperatures. A better recovery may be secured by' passing a current of steam through the bed of leached. sands, using a sufficient pressure of steam to secure the desired rate of flow, and condensing` the eluentfvapors so long as they carry sufficient yammonia to warrant this recovbut this is an expensive procedure in a large operation, inA which it is not unusual I to leach the sands in successive batches of.

about 1000 tons each. rNot only is a large quantity of steam required for heatingthe -sand to thetemperature at whichjsubs'tantial condensation ceases and an eiux of ammonia-bearing vapors begins, but highly expensive pressure-apparatus is required in order to avoid loss of ammonia while introducing the steam at the super-atmospheric pressure necessary for obtaining the desired How through the sand.

According to the present invention we Vovercome the above difficulties in the following manner: After the completion of the yleaching operation proper, and a preliminary washing or washings so conducted as to eliminate the dissolved copperv as far as practicable, we partially exhaust the air from beneath .the sand bed, and allow the bed to drain. Therebvthe dilutecopperbearing solution,I remaining in the inter- Astioes 'ofthe sandis withdrawn, 'and' the sand bed` is leftin a relativelyv .permeable specification of LettersPatent.

on laccount of its ammonia content, as al Wash in the treatment of fresh batches of ore. Meantime the temperature of the sandrises progressively to approximately the y Patented Mar. 30,1920.

Application mea october?, 1919. serial No. 329,179. Y

temperature -of .the steam., and eventually steam appears at the effluent 'surface of the bed. This application of steam is contin.

ued, with condensation of the efliuent va-j l pors, until -theiammonia content of the con? densate falls to al predeterminedy minimum.

We then cut off the direct supply of steam and add water, which is preferably hot, and

is distributed as uniformly as possible oyler the upper surface of the sand bed. partial vacuum being maintained, the water vaporizes rapidly at the diminished pressurev as it percolates through the heated sand, and the resulting steam entrains the last recoverable traces of adsorbed ammonia. The heat necessary for this vaporization is supplied by the ,sand which therefore progressively falls in temperature and is l eventually run to waste.

` This procedure involves certain economic advantages amongwhich are the follow- 1n z The steam is admitted above the sand bed at substantially atmosphereic pressure, and its downward flow is regulated andcontrolled by the suction applied beneath the bed. This renders it possible to simplify very greatly the type and the construction of the apparatus-used, for the reason that the pressure is substantially equal on the inside andoutside ofthe tank covers, and the latter may therefore be of light construction. may be simplyset ina water-seal to avoid losses .of ammonia, and are readily removable for the purpose of filling and emptying the tanks. e y

` 2. The residual heat of the sandis used,

Aunder diminished pressure, to 'generate the steam bywhich'the last recoverable portions of adsorbed ammonia'are eliminated, there-` by avoiding in large measurethe heavy losses of heat which areincurred when-the directly highly heated steamed sand -is run to waste.

Our invention is not limiteo thejtraa ment of copper sands, sincev it may be applied to the treatment of zinc 'or other 'o res or metallurgical products or resldues which are to be subjected to an ammoniacal solvent.

It is especially applicable however to a Iprocess of the general type described 1n S.

Patent 1,131,986, patented March 16, 1915 may be of the same general nature and applied in the same order. f The operation of washing the sands may however be mate-` rially simpliied 'and curtailed, since the final elimination of ammonia is effected by means of steam. Accordingly, we may use one or more leaching solutions as described in the earlier patent. but a more limited volume of wash. Also, the concentration of the leach- I ing solutions may if desired be somewhat higher thanthosedescribed as preferable in said patent.

A preferred leaching cycle will' now be described, it being understood, as stated above, that the procedure of filling the tanks and of iushing out the leached sand differs in no essential respect from that described in the earlier patent. After the sand has beer.` subjected to the action of one or possibly two leaching solutions of cupric ammonium carbonate lwith the result that'substantially all of the copper of the ore has passed into solution, the wash solution containing free ammonia and preferably obtained from the steaming of a previous tank is applied. This wash will displace the 'y greater part of the. copper-bearing solution, and is recovered in the ordinary drain. This wash is followed bv water, 4the purpose of which, as described below, isl to eliminate the copper tosuch lextent that its re-precipitation under the action of steam need not be apprehended. l After the dra-in- ',ing. suction is applied at the bottom of the tank under thefilter, and under the influence. of the vacuum any residue of copper-bearing solution is removed.

4only ammoniawa'sh and water with some ad- The sand nowv contains sorbed ammonia, that is to say ammonia adherent to the surfa of the sand and so strongly held by it t at it cannotbe washed out or displaced in the ordinary way. It is in order toy recover this adherent or adsorbed ammonia that the modified steaming process herein `described is used. Steam at substan tially'atmosphericA pressure is led into the tank above 'the fsan'd, a,

equivalent-for Vexample to about 20" of merway by permitting the sand to vpartial vacuum',

cury, being still maintained beneath the sand bed.

The first into the san by reason of the diminished pressure beneath .the bed are of course con` densed by the cooler sand. After a while,-

however, the sand becomes `thoroughly heated and the steaming is continued until nally steam containing ammonia va or issues from the bottom of the tank. his is condensed and recovered, and the operationl is continued until the condensate contains a predetermined percentage of ammonia, for example about 26%. The supply of steamis then discontinued, the partial vacuum being however still maintained, and water, prefermrtions of the steam flowing ably hot', is admitted at the'surface of the sand. As this water is drawn downward through the heated sand it becomes vaporized under the action of the heat at thereduced pressure, and the flow offammon-iaand water vapor continues until practically all-of the ammonia containedv in and adhering to the sand has been removed. The solution produced during the operating stage in which a vacuum is maintained beneath the `bed is relatively vhigh in ammonia, and is n for this reason advantageously used as a wash fora subsequent cycle. The operation is thus completed and the tank is flushed out in the normal way.

The purpose of the wash which immediately follows the leaching solutions isto remove as much as possible of the copperbearing solution from the` interstices of the sand. Accordingly this wash should contain sufficient free ammonia to prevent precipita# tion of copper from its existing solutions. If steam were admitted directly after the leaching solutions, without an intermediate wash, it would be effective for the removal of ammonia but would re-precipitate the copper as oXid. Similarly, if the water wash wereused directlyfollowing the leaching'solutions, there would be a liability to .the precipitation of a part of the copper in the form after the leaching solutions, first a dilute ammonia wash, and second a certain amount of a water wash. both of these washings pre- .ceding'the application of steam. It'will be understood from the foregoing that the primary purpose of these washes is to eliminate .dissolved copper and to preventits re-precipitation lin the sands.

Certain ofthe advantages of this process may be summarized as follows:

1. The 'advantage to be derived from the use of large tanks with removable covers and with of'tanks because of the factthat inasmuch a single said distributer `for' a row of a basic carbonate. In practice we have found it advisable 'to apply,

as there is no :pressure in the tank' above atmospheric there is accordin ly no necess1ty` for a tight joint between e cover and 130 the tank other than that obtainable by means of a water-seal.

2. The economy the use o water following the steaming of the sand, the vapor resulting from the action of the water on the heated sand'under reduced pressure removing the last traces of ammonia.

3. The employment of the ammonia-bearing condensate recovered in a previous cycle from a body of sand subjected to the action of steam for the recovery of its contained ammonia, as an ammonia-wash in a subsequent` copper under the action of steam.

The accompanying drawing is a diagrammatic iow sheet of the process in its preferred embodiment.

We cla-im:-

1. Process of treating copper-bearing sands or the like, comprising disposing the sand in the. form of a bed or layer, extracting copper therefrom by an ammoniacal solvent, steaming the bed to heat the same, and then vaporizing water in the heated bed under less than atmospheric pressure to recover adsorbed ammonia.

2. In a process of treating copper-bearing sands or the like with an ammoniacal solof steam resulting froml cycle to prevent precipitation of vent, the steps comprising heating the leached sands, and then vaporizing water in the heated sand bed under less than atmospheric pressure to recover adsorbed ammonia.

3. In a process of treating copper-bearing sands or the like with an ammoniacal solvent, the steps comprising admitting steam at substantially atmospheric pressure above thebed of leached sand and establishing a flow of steam downwardly through the bed by means of suction applied beneath the same, thereby heating the bed and extracting ammonia therefrom.

4. In a processof treating copper-bearing sands or the like with an ammoniacal solvent, the steps comprising admitting steam at substantially atmospheric pressure above the bed of leached sand and establishing a flow of'steam downwardly by means of" suction applied beneath the same, thereby heating the bed, and then vaporizing water in the heated bed under less than atmospheric pressure to recover adsorbed ammonia.

lIn testimony whereof, we ailix our signatures.

CENTENNIAL HARRY BENEDICT. HERMAN C. KENNY.

through the bed 

